For the blowing moulding of these hollow bodies, which are blown from thermoplastic preforms which are pre-heated in a heat conditioning oven at a temperature higher than their glass transition temperature but lower than their crystallization temperature, the moulds must be heated by circulating a pressurized temperature-controlled fluid (such as water, which can be at a temperature of up to 90° C., or oil, which can be at a temperature of up to 140° C.). This circuit is partly formed in the mould and partly formed in the mould's respective carrier.
To allow rapid modification of the characteristics of a production line for the purpose of making different hollow bodies, it must be possible to change the moulds quickly. Fluid connection means must therefore be provided between the mould and its carrier to allow continuity of this circuit.
However, the temperature-controlled fluid is under pressure inside the circuit. There is therefore a risk of this fluid spraying out of the carrier when the mould is disconnected from its respective carrier. To solve this problem, it is prior art for the circuit to be fitted with automatic shutoff means. As a rule, these automatic shutoff means are operated automatically whenever the blow-moulding installation is stopped (in an emergency stop, for example, or when a stop is required for maintenance work on the installation). These automatic shutoff means are also tripped when the maintenance worker opens the doors giving access to the heart of the blow-moulding installation.
However, despite the presence of these automatic shutoff means, there is still a risk of hot high-pressure fluid being sprayed out of the carrier when the mould is disconnected in the event that these shutoff means fail and there is residual pressure in the mould.
In addition, the temperature-controlled fluid stays at pressure inside the circuit after the mould has been disconnected from its respective carrier. It is therefore relatively difficult to reconnect the mould to its respective carrier, because considerable force must be exerted against this pressure.
To eliminate this problem and ensure that the temperature-controlled fluid does not remain pressurized inside the circuit formed partly within the carrier, it is known practice to provide a valve for bleeding some of the temperature-controlled fluid from the circuit. This bled fluid is then usually thrown away and lost. This approach is not therefore satisfactory either, especially if the temperature-controlled fluid is oil, the temperature of which may be above 100° C., because bleeding always involves a risk of the liquid being sprayed out and burning the maintenance worker. In any case, this approach is not satisfactory from an environmental point of view.
There is therefore a desire in practice, in the case of these moulding installations, for the mould or each mould to be fitted with a pressurized temperature controlled fluid circuit so designed as to reduce the risk of hot fluid being sprayed out at pressure when the mould is disconnected from its respective carrier, and at the same time for it to be made easier to connect the mould to its carrier.